Conventionally, OTN (Optical Transport Network) has been widely used in large-capacity long-distance optical transport networks. OTN is a technology standardized by the ITU-T. Using a network-monitoring OH (Overhead), OTN facilitates network management and identification of network failure.
Such a network-monitoring OTN-OH includes an OH defined as GCC (Generic Communications Channel) (see FIG. 10). A GCC-OH is used for data transmission such as transmission of control information among OTN apparatuses. Further, the GCC-OH is classified into three types as follows: GCC0 (General Communication Channel 0), GCC1 (General Communication Channel 1), and GCC2 (General Communication Channel 2). Each type of GCC-OH is two bytes.
The GCC0-OH is defined in OTU (Optical Transmission Unit)-OH and used for data transmission between apparatuses at the ends of OTU layer. The GCC1-OH and GCC2-OH are defined in the ODU (Optical Data Unit)-OH and used for data transmission between apparatuses at the ends of ODU layer.
There are two standardized modes for bytes of GCC1 and GCC2: a communication mode with independent 2 Byte×2 Channels (hereinafter, “GCC1/GCC2 mode”), and a communication mode with 4 bytes×1 Channel in which GCC1 and GCC2 are integrated as one channel (hereinafter, “GCC1+GCC2 mode”).
With the GCC1/GCC2 mode, two channels of approximately 1.3 Mbps transmission band are available. With the GCC1+GCC2 mode, one channel of approximately 2.6 Mbps transmission band is available. Communication carriers use the GCC1/GCC2 mode or the GCC1+GCC2 mode depending on the required capacity of band.
Monitoring control on the OTN network is performed with a node on the network designated as GNE (Gateway Network Element) (e.g., a node 1 in FIG. 11), so that a simple management can be provided. Monitoring control on nodes away from the GNE is performed using a GCC.
The OTN network is available usually in the GCC1/GCC2 mode because the load on apparatuses can be suppressed on this mode. However, when a large-capacity file transport has to be performed for upgrading software used by the apparatuses or for other purposes, a wider transmission band is required temporarily. In such a case, the mode is switched to the GCC1+GCC2 mode, and the band thus becomes wider temporarily.
A process for switching the GCC1/GCC2 mode to the GCC1+GCC2 mode or vice versa is described with reference to an example in FIG. 11. For example, in order to switch the GCC mode between a node 2 and a node 5 in FIG. 11, a monitoring control apparatus sends mode-switching commands to both nodes via the GNE using the GCC. Because the mode-switching commands cannot be sent to the two nodes at the exact same instance, the GCC mode of one of the nodes is necessarily switched first.
A configuration and a process for switching the GCC band are described in detail with reference to FIG. 12. As depicted in FIG. 12, a receiving side includes a GCC1-OH extractor, a GCC2-OH extractor, an HDLC (High-Level Data Link Control)-frame constructor, and an HDLC-frame receiver. The GCC1-OH extractor and the GCC2-OH extractor extract a GCC1-OH and a GCC2-OH of 16 bits from an OH part of an input OTN signal, respectively. The 16-bit GCC1-OH parallel data and 16-bit GCC2-OH parallel data are input into the HDLC-frame constructor.
The HDLC-frame constructor converts the 16-bit GCC-OH parallel data into an HDLC frame. Depending on the mode set by the software, the HDLC-frame constructor converts the 16-bit GCC-OH parallel data into an HDLC frame: either an HDLC-frame of 1.3 Mbps×2 Channels on the GCC1/GCC2 mode, or an HDLC frame of 2.6 Mbps×1 Channel on the GCC1+GCC2 mode.
The converted HDLC frame is input to the HDLC-frame receiver. The HDLC-frame receiver performs a termination process on the HDLC frame. Depending on the mode set by the software, the HDLC-frame receiver performs the termination process: the termination process for 1.3 Mbps×2 Channels on the GCC1/GCC2 mode, or a termination process for 2.6 Mbps×1 Channel in the GCC1+GCC2 mode. Reception information encapsulated in the HDLC frame is processed by a CPU using a software.
A transmitting side includes an HDLC-frame generator, a GCC-OH converter, a GCC1-OH insertion unit, and a GCC2-OH insertion unit. The HDLC-frame generator generates HDLC serial data by encapsulating transmission information generated by a software in an HDLC frame.
Depending on the mode set by the software, the HDLC-frame generator generates the HDLC serial data: HDLC serial data of 1.3 Mbps×2 Channels in the GCC1/GCC2 mode, or HDLC serial data of 2.6 Mbps×1 Channel in the GCC1+GCC2 mode. The generated HDLC serial data is input to the GCC-OH converter.
In order to map the HDLC serial data on the GCC1-OH or the GCC2-OH, the GCC-OH converter converts the HDLC serial data into parallel data. The conversion depends on the mode set by the software. On the GCC1/GCC2 mode, the GCC-OH converter converts the serial data of 1.3 Mbps×2 Channels into each 16-bit parallel data.
In the GCC1+GCC2 mode, the GCC-OH converter converts the serial data of 2.6 Mbps×1 Channel into 16-bit×2 parallel data (32 bits in total). The converted 16-bit parallel data is input to the GCC1-OH insertion unit and the GCC2-OH insertion unit. The GCC1-OH insertion unit and the GCC2-OH insertion unit map the input parallel data on the GCC1-OH and the GCC2-OH of the OTN signal (see, for example, Japanese Laid-open Patent Publication No. 2004-266480).
When a monitoring control apparatus performs the process for switching the GCC mode of an apparatus located far away using a technology for a band switching process between the GCC1/GCC2 mode and the GCC1+GCC2 mode described above, transmission is always lost because of inconsistency of the mode between the corresponding apparatuses. Therefore, the process for switching the GCC mode under a monitoring network based on a unified control cannot be efficient.
For example, consider an example depicted in FIG. 11. At the exact moment when the mode of the node 2 is switched from the GCC1/GCC2 mode to the GCC1+GCC2 mode, the mode of the node 2 inevitably becomes inconsistent with the mode of the node 5. As a result, transmission is lost between the monitoring control apparatus and the node 5.
Furthermore, in order to switch the mode of the node 5 to the GCC1+GCC2 mode, GCC transmission between the node 2 and the node 5 needs to be established. However, because the node 5 cannot be accessed from the monitoring control apparatus, there is a possibility that the mode cannot be changed. In order to re-establish transmission to the node 5, the mode of the node 2 needs to be switched back to the GCC1/GCC2 mode. As a result, the mode change for the GCC1+GCC2 mode fails.
Specifically, as depicted in a process configuration in FIG. 12, the GCC modes of the HDLC-frame constructor, the HDLC-frame receiver, the HDLC-frame generator, and the GCC-OH converter are switched so as to switch the GCC band according to instructions from the software. The GCC mode needs to be switched for each individual node.
As described, in order to switch the GCC mode between the corresponding apparatuses that are located far away by the monitoring control apparatus, switching the GCC mode of one of the apparatuses inevitably causes the mode to be inconsistent, and the GCC mode cannot be switched. To perform the GCC mode switching with a conventional configuration, a network operator needs to set a setting of each apparatus locally, each apparatus needs to be connected with the monitoring control apparatus on LAN, or the network needs to be duplicated so as to constitute a redundant GCC configuration. The management of such a network is complex, and equipment investment is increased, which results in higher costs.